M&G won the Outstanding Investment House accolade at last night's OBSR Honours Dinner, held at the Dorchester Hotel in London.
Jim Leaviss, the head of retail fixed interest, collected the award on behalf of the group.
Other winners on the night included Axa's Theo Zemek, who walked away with the Outstanding Contributor to the Industry award.
Aberdeen's Asia Pacific team, led by Hugh Young, won the Outstanding Fund Manager award, beating Jupiter's John Chatfeild-Roberts and Philip Gibbs; Standard Life's Harry Nimmo; and Ian Spreadbury of Fidelity.
The Rising Talent award was presented to Jupiter's Cédric de Fonclare, manager of the European Special Situations fund. Other managers on the shortlist included Neptune's Rob Burnett; Investec's Philip Rodrigs; and Sanjeev Shah of Fidelity.
OBSR research director Richard Romer-Lee says M&G is an outstanding example of a full-service asset manager.
"It is difficult for a fund manager to be good at a lot of things and to be good at running a number of different funds, but M&G has a big range of investment approaches which appeal to wide variety of clients," he says.
"The group reinvigorated itself in the 1990s and adapted itself to be relevant in the modern market.
"M&G has now got a range of very good equity funds, both global and UK. In addition, it was a pioneer of the corporate bond fund and has upped the ante in terms of delivery of performance. It also has some good managed products."
Romer-Lee says Zemek has been a driving force behind the current success of bond funds.
"Theo Zemek has been a fantastic advocate for her asset class. In 1994 when still at M&G, she launched their corporate bond fund at a time when bonds were little appreciated," he says.
"Since then she has worked tirelessly to promote her asset class, educate advisers and support up and coming managers.
"She is also an extraordinary academic, but has succeeded in breaking into the real world and bringing the asset class into mainstream investment. She is also a passionate advocate of the retail market."
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